Part 1. The first part of the research plan is to assess highly attenuated recombinant poxvirus vaccine candidates in the rhesus macaque model. This work is a collaborative effort with Aventis Pasteur, which has a CRADA with the NCI, and involves intra-agency collaboration with the NIAID. Two vectors are being tested: a canarypox-based vector (ALVAC) and the genetically attenuated vaccinia strain (a derivative of the Copenhagen strain) NYVAC. Both vectors are able to complete their replication cycle and express heterologous genes under the control of early or early/late promoters. The working hypothesis is that, because both poxvirus vectors, even in the absence of a complete life cycle, still express a large number of their proteins, the response against the heterologous antigens may be limited. Thus we investigated the hypothesis that conventional DNA plasmid (optimized for expression) may prime immune responses that may further amplify boosting with recombinant poxviruses carrying the same SIV genes. The results obtained indicate that, indeed, priming with DNA and boosting with NYVAC-SIV potentiates the virus-specific immune response at least tenfold (Hel et al., J Immunol 2001). Accordingly, this immunization regimen afforded better containment of viremia following challenge exposure (Hel et al., J Immunol 2002). We are also testing the importance of the addition of all the accessory/regulatory genes to the SIV/HIV structural genes. For this purpose we constructed a novel recombinant protein encompassing the genetic information of rev, nef, and tat devoided of active sites (Hel et al., Vaccine 2002). This recombinant antigen has been used as a vaccine component and recent unpublished data demonstrate that polyvalent vaccines (i.e., those with more antigens) provide better protection. Once an optimal combination of modalities is achieved, other immunization regimens may be further optimized by investigating the importance of the route of immunization and the help of immunomodulatory molecules. Recently, we uncovered that central memory CD8+ T cell responses appear to be more important than effector memory CD8+ T cell responses as the former but not the latter correlated with containment of viral replication (Vaccari et al., unpublished data). Thus, we are investigating strategies to improve central memory responses. Part 2. In view of the encouraging results obtained with a preventive NYVAC-SIV-gag-pol-env vaccine candidate in rhesus macaques, we hypothesized that such a vaccine could also be effective in a regimen of immune intervention following SIV infection. Thus, we develop a model in macaques to test the effect of vaccination in the presence or absence of antiretroviral therapy. A study was designed to assess whether vaccination of macaques treated with antiretroviral therapy could enhance SIV-specific CD4+ T-helper and CD8+ T-cell cytotoxic responses and whether vaccination could increase the ability of the host to maintain viremia at low levels following antiretroviral therapy suspension. The highly attenuated poxvirus NYVAC-SIV-gag-pol-env live recombinant vaccine candidate was chosen as a vaccine approach to test these concepts because of its demonstrated effectiveness as a preventive vaccine candidate in macaques. The results demonstrate the feasibility of establishing an animal model in which immunization and immune intervention could be assessed in a controlled fashion and both CD4+ and CD8+ T-cell responses elicited/boosted by a vaccine in infected animals treated with HAART. This point is very important in the context of the present concern that HAART may silence the immune response to the detriment of the host. The use of this attenuated live vector is safe in animals with active viral replication as well as in HAART-treated macaques, suggesting that the approach may be used in humans. A larger study on efficacy of vaccination in macaques chronically infected with SIVmac251 suggested that vaccination may confer some transient advantage (Tryniszewska et al., J Immunol 2002). Because of the encouraging nature of these results, a safety and immunogenicity trial in HIV-1-infected individuals will be initiated in coming years using a NYVAC-based HIV-1 vaccine. Lastly, the use of cytokines such as IL7 and IL15 as "systemic adjuvants" of vaccines is being investigated. References: Nacsa et al. Virology 2003; Fry et al. Blood 2003; Franchini Clinical and Applied Immunology Reviews 2003; Little et al. Blood 2003; Belyakov et al. PNAS 2003; Radaelli et al. Virology 2003; Edghill-Smith et al. J Infect Dis 2003; Moniuszko et al. J Virol 2003;Franchini et al. in Vande Woude and Klein: Advances in Cancer Research 2003; Nacsa et al. Vaccine 2004; Stevceva et al. Virology 2004; Franchini et al. Expert Rev Vaccines 2004; Moniuszko et al. J Virol 2004. Van Rompay et al. J AIDS in press; Edghill-Smith et al. J Infect Dis in press.